Does anyone have any advice for a beginner to rules (and meteorology)?
Background: I live in the UK, it’s cold and wet here between about October and March, and this means the inside of our car windows tend to mist up over night, when the outside air is cold, particularly if the car is not parked in a garage (as mine isn’t). The simple solution to this is to start the engine a few minutes before leaving, with the fan and A/C on maximum, blowing on the inside of the windscreen. Newer cars have better solutions to this, but my car is old.
From inside my house, I can’t see my car windscreen, when it’s parked on my driveway.
So, what I want is a rule which uses Yahoo weather (or equivalent), to give me a guide as to whether or not my car windscreen is likely to be misted up, and, if so, to set all my downstairs lights (Phillips Hue) to blue a few minutes before my usual departure time, to tell me I need to go outside and start my engine, before finishing the rest of my morning routine. Even better, if I can determine how bad the misting is likely to be, I can have the lights go blue a little earlier or later, so that the windscreen is demisted at just the right time for me to leave.
Now, I’m no meteorology expert, but I believe the key to this will be the dew point - the temperature at which the moisture in the air condenses; if my windscreen is below that value, it will get misted up, and if it’s a long way below that value, it will be heavily misted. Bear in mind the windscreen is colder than the air (I think…), so the temperature of the glass will be below the air temperature.
I found somewhere online an easy way to estimate the dew point from just the temperature and humidity, which, conveniently, Yahoo Weather gives me, which is:
dewPoint = temperature - ((100 - humidity) / 5)
So, my plan is to have a rule which runs every minute for the half-hour before I normally leave for work, which calculates the most up-to-date dew point, as above, and compares it to the air temperature, then applies some kind of fudge factor to come up with a number of minutes before my usual leaving time that I should head out and start my engine.
Does that sound moderately sane?